An aligning agent for lowering the threshold voltage required to effect an optically negative to optically positive phase transition

ABSTRACT

Novel liquid crystalline compositions containing an advantageous aligning agent resin, which causes said compositions, upon application to any suitable substrate to spontaneously align or to have a greater tendency to become aligned in an orientation wherein major axes of the molecules comprising liquid crystalline material are substantially perpendicular to the plane of the substrate. Such liquid crystalline compositions are particularly suited for use in phase transition systems wherein a film comprising cholesteric liquid crystalline material having the tendency to align is transformed to the nematic liquid crystallic state by the application of electrical fields of sufficient field strengths. Such compositions are also used in other liquid crystalline imaging systems making use of differently aligned portions of liquid crystalline films.

KP? 3953 339233 'unuemu one, Haas et al. Oct. 22, 1974 ver [5 ANALIGNING AGENT FOR LOWERING Temperature Nematic Liquid Crystal",Physical Re- THE THRESHOLD VOLTAGE REQUIRED TO EFFECT AN OPTICALLYNEGATIVE TO OPTICALLY POSITIVE PHASE TRANSITION [75] lnventors: WernerE. L. Haas, Webster; James E. Adams, Ontario; Bela Mechlowitz,Rochester, all of NY.

[73] Assignce: Xerox Corporation, Stamford,

,-Conn. [22] Filed: Nov. 9, 1973 [2]] Appl. No.: 414,596

Related U.S. Application Data [62] Division of Ser. No. l73.532, Aug.20, 197i, Pat. No.

[521 U.S. Cl. 350/160 LC, 350/150 [51] int. Cl. G02f l/16 [58] Field ofSearch 350/150, 160 LC [56] References Cited UNITED STATES PATENTS3,652,l48 3/1972 Wysocki et al. 350/l50 3,687,515 8/l972 Haas ct al.350/150 OTHER PUBLICATIONS Haas et al., New ElectroOptic Effect in aRoom view Letters, Vol. 25, Nov, 9, 1970, pp. 1326-1327.

Primary Examiner-Edward S. Bauer Attorney, Agent, or FirmJames J.Ralabate; David C. Petre; Gaetano D. Maccarone [57] ABSTRACT Novelliquid crystalline compositions containing an advantageous aligningagent resin, which causes said compositions, upon application to anysuitable substrate to spontaneously align or to have a greater ten dencyto become aligned in an orientation wherein major axes of the moleculescomprising liquid crystalline material are substantially perpendicularto the plane of the substrate. Such liquid crystalline compositions areparticularly suited for use in phase transition systems wherein a filmcomprising cholesteric liquid crystalline material having the tendencyto align is transformed to the nematic liquid crystallic state by theapplication of electrical fields of sufficient field strengths. Suchcompositions are also used in other liquid crystalline imaging systemsmaking use of differently aligned portions of liquid crystalline films.

14 Claims,.l0 Drawing Figures "aszlazsa PATENTED GET 2 2 i914 ANALIGNING AGENT FOR LOWERING THE THRESHOLD VOLTAGE REQUIRED TO EFFECT ANOPTICALLY NEGATIVE TO OPTICALLY POSITIVE PHASE TRANSITION CROSSREFERENCE TO RELATED CASES This application is a divisional applicationof prior copending application Ser. No. 173,532, filed Aug. 20, 1971,now U.S. Pat. No. 3,803,050.

BACKGROUND OF THE INVENTION This invention relates to liquid crystallinecompositions and imaging systems and, more specifically, to liquidcrystalline compositions including an aligning agent which causes filmsof such compositions to spontaneously align when applied to a suitablesubstrate. Furthermore, the invention includes various spontaneous andelectrical imaging systems embodying the inventive compositions.

Recently, there has been substantial interest in the discovery of moreuseful applications for the class of substances known as liquidcrystals." The name liquid crystals" has become generic to materialswhich exhibit dual physical characteristics, some of which are typicallyassociated with liquids and others which are typically associated withsolids. Liquid crystals exhibit the mechanical characteristics, such asviscosities, which are normally unique to liquids. The opticalcharacteristics of liquid crystals are more similar to thosecharacteristics ordinarily found in the crystalline solid state. Inliquids or fluids, the molecules are typically randomly distributed andoriented throughout the mass of the material. Conversely, in crystallinesolids the molecules are generally rigidly oriented and arranged in aspecific crystalline structure. Liquid crystals resemble solid crystalsin that the molecules of the liquid crystalline compositions areregularly oriented in a fashion analogous to, but less extensive than,the molecular orientation and structure in a crystalline solid. Manysubstances have been found to exhibit liquid crystalline characteristicsin a relatively narrow temperature range. Below that temperature range,the substances typically appear as crystalline solids and above thattemperature range, they typically appear as isotropic liquids.

Liquid crystals are known to appear in three different mesomorphicforms: smectic, nematic and cholesteric. In each of these structures,the molecules are typically arranged in a unique locally symmetricalorientation. In the smectic structure, the molecules are arranged inlayers with their major axes approximately parallel to each other andapproximately normal to the planes of the molecular layers. In thenematic structure, the major axes of the molecules lie approximatelyparallel to each other but the molecules are not organized into definitelayers as in the smectic structure. In the cholesteric structure, themolecules are arranged in definite layers and within a given layer, themolecules are further arranged with their major axes approximatelyparallel to each other and parallel to the planes of the lay ers. In thecholesteric the direction of the major molecular axes is angularlydisplaced from one layer to the next and the direction of thesemolecular axes traces out a helical path through adjacent layers ofmolecules.

The cholesteric structure originally derived its name from the fact thatmaterials exhibiting the cholesteric liquidcrystalline mesophasestrtictur'e are often molecules which are derivatives of cholesterol orwhich are shaped very similarly to molecules of cholesterol.

Liquid crystals have'been found to be sensitive or responsive to avariety of stimuli including temperature, pressure, foreign chemicalcompounds and electric and magnetic fields, as disclosed, for example,in copending application Ser. No. 646,532, filed June 16, 1967, now U.S.Pat. No. 3,804,618; copending application Ser. No. 4,644, filed Jan. 21,1970; French Pat. No. 1,484,584; Fergason U.S. Pat. Nos. 3,409,404 and3,410,999; Fergason et al. U.S. Pat. No. 3,114,836, Waterman et al. U.S.Pat. No. 3,439,525 and Woodmansee U.S. Pat. No. 3,441,513. Mostrecently, imaging systems wherein the imaging member comprises liquidcrystalline material have been discovered and described, for example, incopending applications Ser. No. 821,565, filed May 5, 1969, now U.S.Pat. No. 3,652,148; Ser. No. 849,418, filed Aug. 12, 1969; Ser. No.867,593, filed Oct. 20, 1969, now U.S. Pat. No. 3,642,348; and Ser. No.104,348, filed Jan. 6, 1971, now U.S. Pat. No. 3,666,948.

Cholesteric liquid crystals are known to exhibit various observablealignment states commonly referred to as textures; for example,cholesteric liquid crystals may adopt a homeotropic, a focal-conic or aGrandjean plane texture or alignment state as modifications within thecholesteric mesophase itself. Similarly, nematic liquid crystallinematerials may be aligned parallel to the substrate, normal to thesubstrate (a nematic homeotropic texture), etc. See Gray, G. W.,Molecular Structure and the Properties of Liquid Crystals, AcademicPress, London, 1962, pages 39-54.

In new and growing areas of technology, such as liquid crystals, newcompositions of matter, methods, 'apparatus and articles of manufacturecontinue to be discovered for the application of the new technology andthe new modes. The present invention relates to new liquid crystallinecompositions which cause films of such compositions to spontaneouslyalign and various systems for utilizing and providing images with suchcompositions. I

SUMMARY OF THE INVENTION It is, therefore, an object of this inventionto provide novel compositions having liquid crystalline characteristics.

It is another object of this invention to provide a novel method ofspontaneously aligning films of liquid crystals.

It is another object of this invention to provide novel liquidcrystalline compositions having cholesteric liquid crystalline opticalcharacteristics.

It is another object of this invention to improve the characteristics ofsystems using the cholesteric-nematic phase transformation.

It is still another object of this invention to provide compositionsparticularly suited for transforming optically uniaxial nematiccompositions to optically biaxial nematic compositions.

It is yet another object of this invention to provide novel liquidcrystalline imaging systems.

The foregoing objects and others are accomplished in accordance withthis invention by providing novel liquid crystalline compositionscontaining an advantageous aligning agent, which causes saidcompositions, upon application to any suitable substrate tospontaneously align or to have a greater tendency to become aligned inan orientation wherein major axis of the molecules comprising liquidcrystalline material are substantially perpentlicular to the plane ofthe substrate. Such liquid crystalline compositions are particularlysuited for use in phase transition systems wherein a film comprisingcholesteric liquid crystalline material having the tendency to align istransformed to the nematic liquid crystalline state by the applicationof electrical fields of sufficient field strengths. Such compositionsare also used in other liquid crystalline imaging systems making use ofdifferentially aligned portions of liquid crystalline films.

BRIEF DESCRIPTION OF THE DRAWING For a better understanding of theinvention as well as other objects and further features thereof,reference is made to the following detailed disclosure of preferredembodiments of the invention taken in conjunction with the accompanyingdrawings thereof wherein:

FIG. I is a partially schematic, cross-sectional view of a layer ofliquid crystals on a substrate.

FIG. IA is a magnification of a portion of the view of 7 FIG. I.

FIG. 2 is a partially schematic, cross-sectional view of a layer of thenovel liquid crystalline composition of the instant invention on asuitable substrate.

FIG. 2A is a magnification of a portion of the view of FIG. 2.

FIG. 3 is a partially schematic. cross-sectional view of an imagingmember having imagewise portions comprising the novel liquid crystallinecompositions of the instant invention.

FIG. 4 is a partially schematic top view of the imaging memberillustrated in cross-section in FIG. 3.

FIG. 5 is a partially schematic, cross-sectional view of a liquidcrystalline electro-optic cell.

FIG. 6 is a partially schematic isometric view of an embodiment of aliquid crystalline elcctro-optic imaging cell wherein the desired imageis defined by the shape of the liquid crystalline material as confinedby the shape of the spacing member.

FIG. 7 is a partially schematic isometric view of an embodiment of aliquid crystalline electro-optic imaging cell wherein the desired imageis defined by the shape of at least one of the electrodes.

FIG. 8 is a partially schematic isometric view of an embodiment of aliquid crystalline electro-optic imaging cell between polarizers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the instant invention it hasbeen discovered that novel liquid crystalline compositions which, inaddition to their predominantly liquid crystalline constituent containan advantageous aligning agent which possesses the advantageous propertythat upon application of a film ofsueh composition to a suitablesubstrate, the liquid crystalline composition spontaneously becomesaligned and has a greater tendency to become aligned in an orientationwherein the major axes of the molecules comprising the liquidcrystalline material substantially normal to the plane of the substrate.

It is believed that the presence of the advantageous aligning agent. andnot the influence of the substrate alone. is responsible for thissurprising and advantageous result.

FOr example, FIG. I illustrates in partially schematic. cross-sectionalview (which is not necessarily illustrated in proper proportions). alayer of liquid crystalline material 30 on a suitable substrate 31 andFIG. 1A is a magnification of the encircled portion of the view shown inFIG. 1. In FIG. 1A it is clear that the liquid crystalline materialcomprising the layer 30 itself comprises a number of adjacent domains32. and that within each domain 32, the individual molecules 33 are in aunique locally symmetrical orientation which is characteristic of one ofthe mesomorphic liquid crystalline states. For purposes of illustration,the molecules 33 in FIGS. 1 and 2 are arranged in the locallysymmetrical orientation which is characteristic of the orientation ofthe molecules in the nematic liquid crystalline state although, as willbe discussed below, other liquid crystalline materials in compositionsincluding the advantageous aligning agent of the present inventionbehave in a fashion similar to that illustrated in FIG. 1A.

In FIG. 2, and particularly in FIG. 2A, a layer of liquid crystallinecomposition including the advantageous aligning agent of the instantinvention is illustrated wherein any boundaries between the domains ofmolecules of the liquid crystalline material having the locallysymmetrical orientation are much less definite and the majority of theindividual molecules in the entire layer of liquid crystalline materialare aligned with their major axes substantially normal to the plane ofthe substrate. This direction is schematically shown in FIG. 2 by thearrow 34. It is noted that the advantageous aligning agent of theinstant invention is not specifically illustrated in FIG. 2 and FIG. 2A.However, these aligning agents are typically present in such smallamounts that the illustration of their effect on the molecules of theliquid crystalline material is sufficient to indicate their presence inthe advantageous composition of the instant invention as schematicallyillustrated in FIGS. 2 and 2A.

The advantageous aligning agent of the present invention may compriseand is herein defined to mean any suitable material which, when added toliquid crystalline compositions, causes the liquid crystalline materialcontaining such an aligning agent upon application to a suitablesubstrate to spontaneously align in an orientation wherein the majoraxes of the molecules comprising the liquid crystalline material aresubstantially perpendicular to the plane of the substrate or causes themolecules of the liquid crystalline material to have a greatly increasedtendency to align in that orientation.

The advantageous aligning agents suitable for use in the instantinvention include a wide variety of chemical compounds including avariety of resins and surfactants (surface active agents). Resinssuitable for use as aligning agents include polyamide resins, forexample, Versamid 100, a polyamide resin available from General Mills,Inc, and other Versamid resins such as Versamid I I5, I25 and I40; epoxyresins such as Easypoxy (part 2), available from Conap, lnc.; Dow'sNovolac phenolformaldehyde resins; Polysciences Resin DER 334; CATALYST9, available from Emerson & Cuming; Marsons Fiberglass Epoxy; DupontsElvacite 2046, a n-butylisobutyl methacrylate copolymer and othervarious types of resins including resins and resinous derivatives offatty oils and acids, phenoplasts, aminoplasts, aliphatic amines,glycidyl ethers, polyglycols including amine terminated and epoxyterminated polyglycols, polyols, polysulfides and others.

Other materials which are sometimes identified as surfactants (surfaceactive agents) are also suitable as the advantageous aligning agent inthe instant invention. Such surfactants include esters of polyhydricalcohols, alkorylated amides, esters of polyorypropylene glycols, ethersof polyoxyalkylene glycols, alkylphenyl ethers, tertiary acetylenicglycols, polyoxyethylated alkyl phosphates, carboxylic acids, soaps,sulfonated hydrocarbons and their salts, sulfonated esters, salts,sulfonated amides, and their salts, sulfonatcd amines, and their salts,sulfonated ethers, and their salts, sulfonated carboxylic acids, andtheir salts, sulfonated phenols, sulfonated ligning, acylated aminoacids, acylated polypeptides, phosphates and phosphatides, alkylpolyphosphates, amines and their salts, trialkylamine oxides,polyoxyethylated long-chain amines, quaternary ammonium salts (such astetraalkyl-trialkylarylpolyethoxyethyl-ammonium salts), acylatedpolyamines, and their salts, heterocyclic amines, alkylolamine-fattyacid condensates (i.e., oxazolines), alkyl phosphonamides, amphotericssuch as: cetyl betaine, or sodium N-lauryl-myristyl-B-aminopropionate,sequestrants such as: sodium dihydroxyethylglycinate, or trisodiumnitrilotriacetate and many others.

The above lists of suitable aligning agents are representative ofmaterials suitable for use in the instant invention and are not intendedto be exhaustive or limit- The advantageous aligning agents of thepresent invention are typically added to the liquid crystalline materialin amounts in the range between about 0.1 and about percent by weight,which amounts are typically sufficient to facilitate the advantageousspontaneous alignment.

The advantageous compositions of the instant invention may be preparedby dissolving the liquid crystalline materials or mixtures thereof alongwith the advantageous aligning agent in a suitable solvent, for example,organic solvents such as chloroform, trichloroethylenc,tetrachloroethylene, petroleum ether, methylethyl ketone, isopropanol,toluene and others. The solution containing the liquid crystallinematerial and the advantageous additive is then typically poured, sprayedor otherwise applied to a suitable substrate. After evaporation of thesolvent, a thin layer of liquid crystal containing the aligning agentremains on the substrate. Alternatively. the liquid crystallinematerials along with the aligning agent may be combined and directlyapplied to a suitable substrate by heating the mixed components abovethe isotropic transition temperature of the liquid crystallinecomponents and mixing the components before application to thesubstrate. Room temperature liquid crystals may be used in their naturalroom temperature condition with the advantageous aligning agent mixedtherein. ln embodiments of the present invention where such liquidsolutions or compositions are used in electro-optic cells, suchcompositions maybe injected into position in such electro-optic cells.Many compositions suitable for use herein may have viscosities such thatthe composition layer may have sufficient integrity to beself-supporting on the substrate regardless of the orientation ofthesubstrate.

The liquid crystal layers or films suitable for use in the presentinvention are preferably of a thickness in the range of about 250microns or less, although thicker films mayperform satisfactorily insome embodiments of the instant invention.

"As discussed above herein, nematic liquid crystalline materials,smectic liquid crystalline materials and even cholesteric liquidcrystalline materials, or mixtures thereof, are suitable for use in theadvantageous compositions and various embodiments of the instantinvention. Layers or films of liquid crystalline materials typicallyappear in a non-aligned state wherein the unique direction of the localsymmetry within small domains is randomly different from one domain toanother. However, the presence of the advantageous additives of theinstant invention causes the unique direction of the local symmetry ofthe various domains to substantially align, or to increase theirtendency to align, so thatthe liquid crystalline compositionspontaneously aligns or tends to align in an orientation wherein themajor axes of the molecules are substantially normal to the plane of thesubstrate.

Where the liquid crystalline material is nematic, the materialspontaneously aligns in the nematic homeotropic state wherein the majoraxes of the molecules are substantially normal to the plane of thesubstrate and, consequently, the optic axis of the liquid crystalmaterial is also normal to the plane of the substrate. This effect isillustrated in FIGS. 1, 1A, 2 and 2A. Where nematic liquid crystallinematerials are used in combination with the advantageous aligning agentsof the instant invention, any suitable nematic liquid crystal, mixtureor composition comprising nematic liquid crystals or composition havingnematic liquid crystalline characteristics may be used. Such nematicliquid crystalline materials, include p-azoxyanisole, pazoxyphenetole,p-butoxybenzoic acid, p-methoxycinnamic acid,butyl-p-anisylidene-p-aminocinnamate, anisylidenepara-amino-phenylacetate, pethoxybenzylamino-a-methylcinnamic acid,l,4-bis(pethoxy benzylidene)cyclohexanone, 4,4dihexyloxybenzene,4,4-diheptyloxybenzene, anisal-p-aminoazobenzene, anisaldazine,a-benzeneazo-(anisal-anaphthylamine), n,n'-nonoxybenzetoluidine; anilsof the generic group (p-n-alkoxybenzylidene-p-nalkylanilines), such asp-methoxybenzylidene-p'-nbutylaniline; nematic compounds of thealkoxybenzylidene-aminoalkylphenone group, such asmethoxybenzylidene-amino-butyrophenone andmethoxybenzylidene-amino-valerophenone; mixtures of the above andothers.

Smectic liquid crystalline materials are suitable for use incompositions and systems of the instant invention and their behavior isbelieved to be similar to the behavior of nematic liquid crystallinecompositions including the advantageous aligning agents of the instantinvention. Smectic liquid crystaliine material suitable for use in theinstant invention include: n-propyl-4- ethoxy biphenyl-4-carboxylate;5-chloro-6-n-heptyloxy-2-naphthoic acid; lower temperature mesophases ofcholesteryl octanoate, cholesteryl nonanoate and other open-chainaliphatic esters of cholesterol with chain length of 7 or greater;cholesteryl oleate; sitosteryl oleate; cholesteryl decanoate;cholesteryl laurate; cholesteryl myristate; cholesteryl palmitate;cholesteryl stearate; 4'-n-alkoxy-3'-nitro-biphenyl- 4-carboxylic acids,ethyl-p-azoxy-cinnamate; ethyl-p- 4ethoxybenzylidene-aminocinnamate;ethyl-pazoxybenzoate; potassium oleate; ammonium oleate;

p-n-octyloxy-benzoic acid; the low temperature mesophase ofZ-p-n-alkoxybenzylideneamino-fluorenones with chain length of 7 orgreater; the low temperature mesophase of p-(n-heptyl)oxybenzoic acid;anhydrous sodium stearate; thallium (I) stearate; mixtures thereof andothers,

Surprisingly, even cholesteric liquid crystalline materials, wherein theunique local symmetry of the molecules is such that the direction of themajor axes is angularly displaced from one layer of molecules to thenext, are affected by the addition of the advantageous aligning agentsof the instant invention. While it is not practically possible for thealigning agents alone to transform the cholesteric molecular arrangementinto an aligned state resembling the aligned nematic state, it has beenfound, surprisingly, that the presence of the advantageous aligningagents of the instant invention facilitate the electrical phasetransformation of an initially cholestcric liquid crystalline state intothe nematic liquid crystalline state. This phase transformation systemis discussed in detail below herein. Any suitable cholesteric liquidcrystalline material or mixture or composition comprising liquidcrystals having cholesteric liquid crystalline characteristics may beused in the compositions and systems of the instant invention.Cholesteric liquid crystalline materials suitable for use in the instantinvention include derivatives from reactions of cholesterol andinorganic acids; for example, cholesteryl choloride, cholesterylbromide, cholesteryl iodide, cholesteryl fluoride. cholesteryl nitrate;esters derived from reactions of cholesterol and carboxylic acids; forexample, cholesteryl crotonate; cholesteryl nonanoate, cholesterylhexanoate; cholesteryl formate; cholesteryl docosonoate; cholesterylehloroformate; cholesteryl propionate; cholesteryl acetate; cholesterylvaleratc; cholesteryl vaccenate; cholesteryl linoleate; cholesteryllinolenate; cholesteryl olcate; cholesteryl erucate; cholesterylbutyrate; cholesteryl caprate; cholesteryl laurate; cholesterylmyristate; cholesteryl clupanodonate. ethers of cholesterol suchcholesteryl decyl ether; cholesteryl lauryl ether: cholesteryl oleylether; cholesteryl dodeeyl ether; carbamates and carbonates ofcholesterol such as cholesteryl decyl carbonate; cholesteryl oleylcarbonate; cholesteryl methyl carbonate; cholesteryl ethyl carbonate;cholesteryl butyl carbonate; cholesteryl docosonyl carbonate;cholesteryl cetyl carbonate; cholesteryl-p-nonylphenyl carbonate;cholcsteryl-2-(2-ethoxyethoxy)ethyl carbonate;cholesteryl-2-(Z-butoxyethoxy) ethyl carbonate;cholesteryl-2-(2-methoxyethoxy)ethyl carbonate; cholesteryl hcptylcarbamate; and alkyl amides and aliphatic secondary amines derived from38 amino- A-S-cholcstene and mixtures thereof; peptides such ascholesteryl polyy-benzyll-glutamate derivatives of beta sitostcrol suchas sitostcryl chloride; and active amyl ester of cyanobenzylidene aminocinnamate. The alkyl groups in said compounds are typically saturated orunsaturated fatty acids, or alcohols. having less than about 25 carbonatoms and unsaturated chains of less than about 5 double-bonded olefinicgroups. Aryl groups in the above compounds typically comprise simplysubstituted bcnzene ring compounds. Any of the above compounds andmixtures thereof may be suitable cholesteric liquid crystallinematerials in the ad vantageous compositions and systems of the presentinvention.

The above lists of materials exhibiting various liquid crystallinephases are not intended to be exhaustive or limiting. The lists disclosea variety of representative materials suitable for use in theadvantageous compositions and systems of the instant invention.

The substrate upon which the advantageous compositions of the instantinvention spontaneously align may comprise any suitable material, and invarious embodiments, may be in any desired form, shape or orientation.For example, the substrate may comprise electrically conductivematerials such as copper, brass, aluminum, steel, cadmium, silver, gold,tin or others. Similarly, the substrate may comprise electricallyinsulating material such as glass, plastic, papers, ceramics or othersuitable insulators. In still other substrates a conductive substratemay be coated onto an insulator, for example, NESA glass, which is apartially transparent tin oxide coated glass which is available from thePittsburgh Plate Glass Co. Another such substrate comprises aluminizedMylar made up of a Mylar polyester film available from DuPont, having athin, semitransparent aluminum coating. Another such substrate comprisesMylar coated with copper or copper iodide. In addition to theserepresentative substrate materials, any other suitable material may beused.

In another preferred embodiment of the advantageous system of thepresent invention, the novel compositions which spontaneously align maybe overcoated with any suitable material, typically a transparentmaterial, or may be sandwiched between two layers of any desiredmaterial. For example, a spontaneously aligned or spontaneouslyalignable composition on a suitable substrate may be overcoated with amaterial such Tedlar, a polyvinyl fluoride, available from DuPont;polyethylene film; polyvinylchloride film; Mylar, a polyester resin filmavailable from DuPont, thin glass plates and sheets, mixtures thereofand others. Such overlayers are typically transparent films.

In the modes of the instant invention where the liquid crystallinecompositions actually spontaneously align when placed on a substrate,for example. a nematic material doped with an advantageous aligningagent, visual differences appear in the liquid crystalline material ineither reflected or transmitted light. For example, the nematic materialin the aligned state is more transparent than in the non-aligned stateand contrast between aligned and non-aligned portions of a layer ofliquid crystalline material may be enhanced with polarizers or othercontrast enhancing means.

The differentially optically reflective and transmissive properties ofspontaneously aligned and nonaligned portions ofa layer ofliquidcrystalline composi tion may comprise an imaging system. For example,the imaged member illustrated in FIGS. 3 and 4 comprises substrate 31supporting liquid crystalline layer 35 comprising imagewise portions 36which include the advantageous aligning agent of the instant inventionand background portions 37 which are in a non-aligned state. Suchimagewise layers of liquid crystals may also be used in liquidcrystalline electro-optic cells to light,

enhance or color such images. For example, these liquid crystallinecompositions maybe used in conjunction with the photoconductivesubstrate as shown in copending application Ser. No. 51,258, filed June30, 1970, now U.S. Pat. No. 3,671 ,23 l. The inventive compositions alsoprovide heretofore unknown advantages in liquid crystalline'electro-optic cells, for example, like the ones illustrated in FIGS.-8.

Among the effects known to be useful in such electro-optic liquidcrystalline cells are dynamic scattering in nematic liquid crystallinecompositions. temporary color changes (pitch changes) in cholestericliquid crystalline materials; texture transition effects in cholestericliquid crystalline materials; and even cholestericnematic phasetransition effects in initially cholesteric liquid crystallinematerials. ln various embodiments of these and other liquid crystallineelectro-optic systems, the ability to spontaneously align the liquidcrystalline material before the use of the electro-optic effects, canproduce novel and advantageous results. For example, a layer of nematicliquid crystalline material which is initially optically uniaxial withthe optic axis normal to the plane of the layer may have an electricalfield applied perpendicular to the optic axis of the composition layerthereby inducing optical biaxiality in the liquid crystallinecomposition. This effect is discussed at length in copending applicationSer. No. 104,328, filed Jan. 6, 1971. the entire disclosure of which ishereby expressly incorporated by reference in the instant application.

Similarly. the increased tendency of films of cholesteric liquidcrystalline materials to align is highly desirable in reducing the totalelectrical energy necessary for producing the advantageouscholesteric-nematic phase transformation in initially cholesteric liquidcrystalline materials. The advantageous phase transformation isdescribed in great detail in copending application Ser. No. 821,565,filed May 5, 1969, now US. Pat. No. 3,652,148, the entire discosure ofwhich is hereby expressly incorporated by reference in the instantapplication. As discussed earlier herein, pure cholesteric materialscontaining the advantageous aligning agents typically do notspontaneously align but their reduction of the total energy needed toperform the cholestericnematic phase transition clearly indicates theincreased tendency of these novel compositions to align.

The following examples specifically define the present invention withrespect to novel liquid crystalline compositions and alignment systems.The parts and percentages in the disclosure, examples and claims are byweight unless otherwise indicated. The examples are intended toillustrate various preferred embodiments of the inventive system forproviding novel liquid crystalline compositions and aligning such liquidcrystalline compositions spontaneously on a suitable substrate.

EXAMPLE 1 A nematic liquid crystalline mixture comprisingpmethoxybenzylidine-p'-butylaniline (hereafter ABUTA) is doped withabout 0.5 percent Versamid 100, a polyamide resin available from GeneralMills, lnc., and this composition is spread on a thin film on a standardmicroscope slide. The nematic liquid crystalline composition containingthe aligning agent spontaneously aligns in a nematic homeotropic texturewherein the major axes ofthc molecules comprising the nematic liquidcrystalline material are substantially perpendicular to the plane of thesubstrate.

EXAMPLES 11, Ill & IV

A nematic liquid crystalline composition comprising ABUTA as in Example1 is doped with about 1 percent of Versamid resins 15, 125, 140,available from Genera l lvlills, lnc., and the three separate samplesspontaneously aligned as in Example 1.

EXAMPLES V-XII 1n Examples V-Xll, a thin line ofthe specific aligningagent is placed on a microscope slide and a drop of ABUTA is placed overthe thin line of the aligning agent thereby allowing the agent and thenematic liquid crystalline material to mix at their interface to anextent not greater than about 10 percent by weight of the aligningagent.

V. Easypoxy (Part 11), an epoxy resin avilable from CONAP. lnc.

Vl. Catalyst 9, an epoxy resin available from Emerson & Cuming.

Vll. Novalac, phenyl-formaldehyde resin available from Dow ChemicalCompany.

Vlll. Resin DER 334, an epoxy resin available from Polysciences.

1X. Fiber glass epoxy. available from Marson's.

X. Elvacite 2046. an n-butyl/isobutyl methacrylate copolymer availablefrom DuPont.

Xl. Diethylenetriamine, T4573, available from Eastman Chemicals.

Xll. Triethylenetetraamine, P4572, available from Eastman Chemicals.

In each case the liquid crystalline material doped by the aligning agentassumes the aligned orientation wherein major axes of the moleculescomprising nematic liquid crystalline material are substantiallyperpendicular to the plane of the substrate.

EXAMPLES XIll-XXXl A thin line of each one of the surfactant typealigning agents is placed on a standard microscope slide and a drop ofABUTA placed on the line of the aligning agent.

Xlll. Sulfated nonylphenyl ether tetraethylene glycol ammonium salt.

XIV. Polyoxyethylated nonyl phenol (alkylphenyl ether) XV. Zincnaphthenate XVl. Cobalt naphthenate XVll. Sulfated nonylphenyl ethertetraethylene glycol NH, salt, ALlPAL CO-436, available from GAF XVlll.Polyoxyethylated nonyl phenol (alkylphenyl ether) Gepal Co-630,available from GAF XlX. Zinc naphthenate XX. Cobalt naphthenate XXl.Polyoxyethylated lauric acid, aldosperse L-9, available from GlycoChemical, lnc.

XXll. Diethylene Glycol Monolaurate, Pegosperse ml. available from GlycoChemical, lnc.

XXlll. Diethylene Glycol Monooleate, Pegosperse 100, available fromGlyco Chemical, lnc.

XXIV. N-polyethoxylated Coco amine, ethomeen C/25, available from Armourlnc. Chem. Co.

XXV. Surfynol 104, a tertiary acetylenic glycol, available from Air Red.Chem. Co.

XXVl. Arlacel 186, a tertiary acetylenic glycol, available from AtlasChemical lnc.

XXVll. Atlas G3300, a tertiary acetylenic glycol, available from AtlasChemical lnc.

XXVlll. Nonylphenoxypoly(ethylenoxy) ethanol XXlX. Sulfatedpolyoxyethylated nonylphenol sodium salt XXX. Polyoxyethylatednonylphenol XXXl. FC J46, afluorochemical compound, available from Minn.Mining & Mfg. Co.

EXAMPLE XXXll A liquid crystalline electro-optic cell is prepared byfirst preparing a mixture of liquid crystalline materials comprisingabout 35 percent cholesteryl chloride and about 65 percent of a mixtureof p-ethyoxybenzylidene-p'-n-butylaniline (EOBUTA) and pbutoxy,benzylidene-p'-n-butylaniline (BOBUTA), which is a mixture of materialswhich has cholesteric liquid crystalline characteristics. Four parts ofthis mixture are then mixed with one part of a composition comprisingABUTA and about 2 V2 percent of the aligning agent Versamid 100. apolyamide resin available from General Mills, Inc. A layer of thealigning agent doped eholesteric liquid crystalline mixture is placedbetween and in contact with a pair of substantially transparentelectrodes of tin oxide coated glass. The transparent electrodes areseparated by an about one-half ml thick Tedlar (polyvinyl fluoride,commercially available from DuPont) spacer and the electrodes areconnected in circuit with an electrical generator. When an electricalfield provided by placing a voltage of about 275 volts DC is placedacross this sample. the electrical field-induced cholestericnematicphase transition occurs, as described in copending application Ser. No.821,565, filed May 5, 1969, now US. Pat. No. 3,652,148.

As a control cell. a second cell having the same component mixturewithout the Versamid 100 aligning agent is used and it is found that theelectrical fieldinduced cholesteric-nematic phase transition thresholdvoltage is about 400 volts DC. It is therefore clear that the additionof the advantageous aligning agent of the instant inventionsignificantly reduces the total electrical energy necessary to achievethe cholesteric-nematic phase transition.

Although specific components, proportions, arrangements and conditionshave been stated in the above description of preferred embodiments ofthis invention, other suitable materials and procedures such as thoselisted above. may be used with satisfactory results and variations inthe system may be made to synergize, enhance or otherwise modify theproperties of or increase the uses for the inventive system. It will beunderstood that such other changes in the details, materials, steps,arrangements of parts and uses which have been herein described andillustrated in order to explain the nature of the invention will occurto and may be made by those skilled in the art upon a reading of thisdisclosure and such changes are intended to be included within theprinciple and scope of this invention.

What is claimed is:

1. A method for producing an optically negative to optically positivephase transition in an initially optically negative liquid crystallinecomposition comprisproviding an optically negative liquid crystallinecomposition comprising cholesteric liquid crystal line material and analigning agent which tends to align the molecules of the cholestericliquid crystalline material;

providing a layer of said liquid crystalline composition on a substrate;and

applying an electrical field across said liquid crystalline ayer W1 inthe optically negative-optically positive phase transition electricalfield strength range of said liquid crystalline composition.

2. The method as defined in claim 1 wherein said electrical fieldapplied across said liquid crystalline layer is in imagewiseconfiguration, whereby said liquid crystalline composition is imagewisetransformed.

3. The method as defined in claim 1 wherein said aligning agentcomprises from about 0.1 percent to about 10 percent by weight of saidliquid crystalline composition.

4. The method as defined in claim 1 wherein said layer of liquidcrystalline composition is provided in a thickness not greater thanabout 250 microns.

5. The method as defined in claim 1 wherein said aligning agentcomprises a surfactant material.

6. The method as defined in claim 5 wherein said surfactant materialcomprises a polyamide resin.

7. The method as defined in claim 1 wherein the optically negativeliquid crystalline composition additionally includes nematic liquidcrystalline material.

8. The method as defined in claim 1 additionally comprising providing apair of electrodes at least one of which is substantially transparent onopposite sides of said layer of liquid crystalline material andproviding a source of electrical potential difference operativelyconnected to said electrodes, whereby said electrical field is appliedacross said liquid crystalline-material.

9. The method as defined in claim 8 wherein said electrical fieldapplied across said liquid crystalline layer is in imagewiseconfiguration. whereby said liquid crystalline composition is imagewisetransformed.

10. The method as defined in claim 9 wherein said aligning agentcomprises from about 0.1 percent to about 10 percent by weight of saidliquid crystalline composition.

11. The method as defined in claim 9 wherein said layer of liquidcrystalline composition is provided in a thickness not greater thanabout 250 microns.

12. The method as defined in claim 9 wherein said aligning agentcomprises a surfactant material.

13. The method as defined in claim 12 wherein said surfactant materialcomprises a polyamide resin.

14. The method as defined in claim 9 wherein said optically negativeliquid crystalline composition additionally includes nematic liquidcrystalline material.

1. A METHOD FOR PRODUCING AN OPTICALLY NEGATIVE TO OPTICALLY POSITIVEPHASE TRANSITION IN AN INITIALLY OPTICALLY NEGATIVE LIQUID CRYSTALLINECOMPOSITION COMPRISING PROVIDING AN OPTICALLY NEGATIVE LIQUIDCRYSTALLINE COMPOSITION COMPRISING CHOLESTERIC LIQUID CRYSTALLINEMATERIAL AND AN ALIGNING AGENT WHICH TENDS TO ALIGN THE MOLECULES OF THECHOLESTERIC LIQUID CRYSTALLINE MATERIAL; PROVIDING A LAYER OF SAIDLIQUID CRYSTALLINE COMPOSITION ON A SUBSTRATE; AND APPLYING ANELECTRICAL FIELD ACROSS SAID LIQUID CRYSTALLINE LAYER WITHIN THEOPTICALLY NEGATIVE-OPTICALLY POSITIVE PHASE TRANSITION ELECTRICAL FIELDSTRENGTH RANGE OF SAID LIQUID CRYSTALLINE COMPOSITION.
 2. The method asdefined in claim 1 wherein said electrical field applied across saidliquid crystalline layer is in imagewise configuration, whereby saidliquid crystalline composition is imagewise transformed.
 3. The methodas defined in claim 1 wherein said aligning agent comprises from about0.1 percent to about 10 percent by weight of said liquid crystallinecomposition.
 4. The method as defined in claim 1 wherein said layer ofliquid crystalline composition is provided in a thickness not greaterthan about 250 microns.
 5. The method as defined in claim 1 wherein saidaligning agent comprises a surfactant material.
 6. The method as definedin claim 5 wherein said surfactant material comprises a polyamide resin.7. The method as defined in claim 1 wherein the optically negativeliquid crystalline composition additionally includes nematic liquidcrystalline material.
 8. The method as defined in claim 1 additionallycomprising providing a pair of electrodes at least one of which issubstantially transparent on opposite sides of said layer of liquidcrystalline material and providing a source of electrical potentialdifference operatively connected to said electrodes, whereby saidelectrical field is applied across said liquid crystalline material. 9.The method as defined in claim 8 wherein said electrical field appliedacross said liquid crystalline layer is in imagewise configuration,whereby said liquid crystalline composition is imagewise transformed.10. The method as defined in claim 9 wherein said aligning agentcomprises from about 0.1 percent to about 10 percent by weight of saidliquid crystalline composition.
 11. The method as defined in claim 9wherein said layer of liquid crystalline composition is provided in athickness not greater than about 250 microns.
 12. The method as definedin claim 9 wherein said aligning agent comprises a surfactant material.13. The method as defined in claim 12 wherein said surfactant materialcomprises a polyamide resin.
 14. The method as defined in claim 9wherein said optically negative liquid crystalline compositionadditionally includes nematic liquid crystalline material.